Up to 135,000 retired married women could be owed £135 million in underpaid state pensions after an investigation showed “shocking” failures in the system.

The women had made small National Insurance contributions for much of their adult lives and therefore have smaller state pensions. They should, however, have had payments topped up by the government when their husbands with full national insurance contributions — spanning 44 years in most cases — reached 65, guaranteeing them 60 per cent of the basic state pension.

An investigation has found that thousands of women have not claimed this as required if their husband reached retirement age before March 2008. Thousands more whose husbands retired after that date have also missed out on what should have been an automatic